1. Field of the Invention
The present invention relates to a method for extrusion-molding a laminated parison and an apparatus for the same. More specifically, the present invention relates to a method for extrusion-molding a laminated parison and an apparatus for the same, which is used for molding a vessel possessing highly effective barrier properties to gasohol containing alcohol, for example, a plastic automotive fuel tank.
2. Description of the Related Art
As disclosed in Japanese Patent Application Laid-open No. 99475/97, the applicant has previously proposed a method of and an apparatus for extrusion-molding a laminated parison which have the following arrangement and function. That is, FIG. 1 shows a whole schematic arrangement of the prior art apparatus for extrusion-molding the laminated parison. FIG. 2 is a cross sectional view of a multi-ring structure shown in FIG. 1.
In FIG. 1, reference numeral 1 denotes a die head having an approximately cylindrical shape as a whole. A head core 4 is provided in a head body 2 of the die head 1. An annular multi-ring structure 12 is provided therebetween. A cylindrical inner main material flow passage 47 is provided on the head core 4 side of the multi-ring structure 12. An outer main material flow passage 48 is provided on the head body 2 side thereof. These main material flow passages 47 and 48 are communicated with to a main material extruder 41 provided on an upper portion of an outer wall of the die head 1.
The main material flow passages 47 and 48 are communicated with an extrusion nozzle 30 formed by die outer and inner cylinders 28 and 29, respectively, mounted on lower portions of the head body 2 and the head core 4. The inner cylinder 29 is moved upwardly and downwardly through a vertical rod 31, and thereby a nozzle gap of the extrusion nozzle 30, that is, a wall thickness of the laminated parison can be freely adjusted.
As shown in FIGS. 1 and 2, the multi-ring structure 12 comprises first, second and third spider rings 50, 51 and 52 forming a spider 49, and a cap ring 53. First, second, third and fourth annular nozzles 16, 17, 18 and 46 are concentrically provided in the spider rings 50, 51, 52 and the cap ring 53.
The first and third annular nozzles 16 and 18 are communicated with an adhesive material extruder 19. The second annular nozzle 17 is also communicated with a barrier material extruder 20 which is for extruding a barrier material made of well-known ethylene-vinyl-alcohol copolymer resin (abbreviated EVOH) which possesses barrier properties to gasohol containing alcohol. The main material flow passages 47, 48 and the annular nozzles 16, 17, 18, 46 are concentrically arranged in the die head 1.
The fourth annular nozzle 46 is communicated with a groove 6b formed between the cap ring 53 and the first spider ring 50. The fourth annular nozzle 46 is formed so that it may be situated to face the inside of the outer main material flow passage 48. The groove 6b is communicated with, through a flow passage 6a, a reclaimed material extruder 6 which is for extruding a reclaimed material so as to make it lamina-shaped, which is obtained by crushing burrs reclaimed from molded products.
An operation will be described below. In the first place, the extruders 41, 19, 20 and 6 are driven by respective drivers (well-known hydraulic cylinders or rotating apparatus) 42, 43, 44 and 45. By the thus driven extruders, inner and outer main materials A and F, first and second adhesive materials B and D, a barrier material C and a reclaimed material E are intermittently or continuously extruded and supplied into the inner and outer main material flow passages 47 and 48 and into the annular nozzles 16, 18, 17 and 46, respectively. A four-different-material six-layered laminated parison 32 is thus obtained from the extrusion nozzle 30. The parison 32 has a wall structure consisting of six layers: innermost and outermost layers of the inner and outer main materials A and F, respectively; a core layer of the barrier material C which is a core material; a pair of first and second adhesive material layers B and D, respectively, the first adhesive material layer B being situated between the inner main material layer A and the barrier material layer C, the second adhesive material layer D being situated between the outer main material layer F and the barrier material layer C; and a layer of the reclaimed material E situated between the outer main material layer F and the second adhesive material layer D.
By performing blow molding for the laminated parison 32 by means of a blow molding apparatus not shown, a container, e.g. a gasoline tank, having a four-different-material six-layered wall structure can be molded, which includes the core layer of the barrier material which exhibits barrier properties to methanol, ethanol or the like. A container will advantageously be achieved, which includes the highly effective barrier material, for example, ethylene-vinyl-alcohol copolymer resin or EVOH and was heretofore impossible to achieve.
The aforementioned method for extrusion-molding the laminated parison and the apparatus for the same has the following problems caused by the above-described arrangement. That is, as shown in FIG. 3, the thickness of the outer main material layer becomes non-uniform in a spider portion G in a circumferential section of the laminated parison 32. Furthermore, the outer and inner main materials F and A are supplied from a single extruder and separated by the multi-ring structure, and thus the laminar thickness cannot be independently controlled.
Moreover, when the extruders are continuously driven so as to continuously extrude the four-different-material six-layered laminated parison 32 from the extrusion nozzle 30 of the die head 1, as shown in FIG. 4, an intermediate material layer I is sometimes waved in a circumferential shape, where the intermediate material layer I consists of the barrier material C and the first and second adhesive materials B and D formed inside and outside the barrier material layer C, respectively.